Principles and applications of electrochemical capacitors

Carbon materials for the electrochemical storage of energy in capacitors

Influence of oxygen treatment on electric double-layer capacitance of activated carbon fabrics

Supercapacitors or electrochemical double-layer capacitors (EDLCs) have capacitance value up to thousands of Farads at the same size as for conventional capacitors. At such capacitance value EDLCs are of interest for electrical energy storage. The specific energy of commercial supercapacitors is limited to 5–6 Wh/kg, whereas for batteries the lower limit is 35–40 Wh/kg. Nonetheless other advantages of supercapacitors make them already useful in conjunction with batteries in power applications. Main results related to supercapacitor performance improvement available in literature are presented. Research efforts have been done to increase the specific capacitance of supercapacitor electrodes based on activated or porous carbon material, already used in commercial products. By using available activated carbon with a specific surface area reaching 3000 m 2 /g, specific capacitance values up to 300 F/g have been reported for the investigated experimental supercapacitors. Nonetheless, further optimization of activated carbon properties and its use in supercapacitor electrodes is required for 300 F/g and higher value. By addition of metallic oxides or conductive polymers in the activated carbon used for EDLC electrodes, specific capacitance enhancement takes place. Carbon nanotubes used in experimental supercapacitor electrodes resulted in specific capacitance as high as 180 F/g but higher electrical conductivity and consequently, specific power than in the case of activated carbon was observed. Addition of a small percent of carbon nanotubes in the activated carbon for electrodes results in performance improvement (higher capacitance and conductivity). Nevertheless, high cost of carbon nanotubes prevents their use in commercial products.

On the performance of supercapacitors with electrodes based on carbon nanotubes and carbon activated material—A review

Polythiophene-based supercapacitors

Fabrication of high-power electric double-layer capacitors

An activated carbon/polyacene composite is disclosed. The composite contains activated carbon powder or fiber and having a selected molar ratio range of hydrogen atoms [H] to carbon atoms [C] of 0.01≦[H]/[C]≦0.2. It provides two or more times the capacitance per unit volume, and enables reduction of the equivalent series resistance of an electric double-layer capacitor without compression. It therefore is a suitable composite for use as polarizable electrodes for electric double-layer capacitors. The composite can be made by mixing activated carbon powder or fiber and a thermosetting resin powder such as phenolin resin powder, and subjecting the mixture to heat treatment in a nonoxidizing atmosphere at temperatures between 600° and 1000° C. which is insufficient to reach full carbonization of the thermosetting resin.

Activated carbon/polyacene composite and process for producing the same

A unitary-formed electrode structure serving as both a collector and a polarization electrode includes an electrically conductive base serving as the collector, and a polarization electrode that includes a multiplicity of separate polarization particles dispersed throughout the base and exposed in at least a part of a surface of the base.

Electric double layer capacitor and method of forming the same

An electric double-layer capacitor with large capacitance, 1000 F at 5.5 V, has been developed. It uses activated carbon/carbon (AC/C) composite as the polarizable electrodes and sulfuric acid as the electrolyte. The AC/C composite was synthesized through a simple process, namely, a cured mixture of activated carbon and phenol-formaldehyde resin was carbonized. The AC/C composite has a large surface area, 1300 mg, and low resistivity, 0.01 Omega -cm. Two kinds of pores exist in the AC/C composite: macropores with submicrometer diameters, and micropores with below 4-nm diameter. The micropores are impregnated with the sulfuric acid aqueous solution through the macropores open to the outer surface. The electric double-layer capacitance per unit volume for the AC/C composite in sulfuric acid is greater than that for activated carbon powder as a raw material. The capacitor is expected to be used as an energy storage device and a supplementary power source. >

Large capacitance electric double layer capacitor using activated carbon/carbon composite

An electric double-layer capacitor (EDLC) has a laminated overcoat encapsulating a stacked body including a plurality of basic cells and a pair of terminals sandwiching therebetween the stacked body The innermost film of the laminated overcoat is thermally fused onto the exposed surfaces of the terminal plates and the stacked body substantially without a gap The fusing step is conducted by an equal-pressure pressing using a hot water while the internal of the laminated overcoat is evacuated

Takashi Saito

Papers

Fabrication of high-power electric double-layer capacitors

Activated carbon/polyacene composite and process for producing the same

Electric double layer capacitor and method of forming the same

Large capacitance electric double layer capacitor using activated carbon/carbon composite

Electric double-layer capacitor having a laminated overcoat